1. Field of the Invention
The present general inventive concept relates to a method and device to generate a position profile using lower-order polynomials in a motion controller.
2. Description of the Related Art
An industrial articulated robot moves a work subject to a target position by rotating and moving its joints, and includes a servomotor as a drive source for moving each joint.
A motion controller generates a position profile using an input command and transfers it to a servo controller. The servo controller then controls the servomotor according to the position profile to move the work subject to the target position. The position profile is used to determine work pattern and time in controlling the servomotor of the articulated robot.
Methods for generating a position profile in the motion controller are typically based on integration or polynomials.
As shown in FIG. 1, the integration-based position profile generation method generates an acceleration/deceleration (acc/dec) pattern by integrating a jerk pattern, and generates a velocity pattern by integrating the acc/dec pattern, and then generates a position profile by integrating the velocity pattern.
It is relatively easy to implement the integration-based method. However, this method requires a large amount of variables to be stored for calculation in the integration procedure. It is also difficult for this method to implement asymmetrical acceleration/deceleration, and calculation errors may occur.
As shown in FIG. 2, the polynomial-based position profile generation method typically generates a position profile by selecting a polynomial from seven polynomials P(0) to P(6) for each section of the position profile according to the condition of each section. Here, a calculation for generating the position profile is performed for each section. For example, seven different types of sections of a position profile may be defined as the following seven 3rd-order polynomials P(0) to P(6) with time variables (ta, a=0, 1, 2, 3) and coefficients (Cxy).P(0)=C00+C01t+C02t2+C03t3 P(1)=C10+C11t+C12t2 P(2)=C20+C21t+C22t2+C23t3 P(3)=C30+C31t P(4)=C40+C41t+C42t2+C43t3 P(5)=C50+C51t+C52t2 P(6)=C60+C61t+C62t2+C63t3 
However, the conventional polynomial-based method requires a large number of coefficients for defining polynomials according to initial conditions, so that the calculation of the coefficients according to initial conditions is complicated, and a large amount of real-time calculation is needed.